Tegretol (CBZ) pharmacokinetics were determined in patients undergoing treatment for mania and depression. A HPLC method was developed to analyze CBZ and its epoxy metabolite in plasma and CSF. Levels of CBZ for routine clinical use was determined by EMIT. It was found that, although the levels of CBZ or its epoxide in plasma have no correlation with the efficacy of CBZ among various patients, in the patients that do respond, CBZ plasma levels gave good correlation with the clinical improvement of the patient.